1. Field of the Invention
The present invention relates to an information transmitting apparatus, and more particularly to such an apparatus for transmitting image information or the like through a transmission channel composed for example of optical fibers.
2. Description of the Prior Art
There are recently proposed various information transmitting systems for transmitting image information or the like between distant locations. A recent example of the channel for such transmission is optical fibers for achieving high-speed transmission and avoiding external perturbations. As an example of the applications of such system, there is known the so-called local area network for information transmission among plural locations within a limited area such as a building or a business facility.
In a so-called loop transmission system in which plural terminal units are connected as a loop, for example through optical fibers, the function of the entire system is ensured only when the electric power supplies at these terminal units are all turned on to energize all the interface units including the opto-electric (O/E) converters and electro-optical (E/O) converters. Stated differently, in case one of the terminal units is not operable, for example by a failure in the power supply thereto, by a failure in the terminal unit itself or because power has not been turned on for the terminal unit due to the absence of demand for using that terminal unit, the transmission of information is interrupted at such disabled terminal unit and the function of the entire system is therefore disabled.
Also there are known certain information transmitting systems in which each terminal unit is provided with a back-up power source for replacing the normal power supply in case of a failure therein. Such a terminal unit is designed to be energized by the back-up power source in case of a failure in the normal power supply. Such a back-up power source is generally controlled by the status of power supply to the corresponding terminal unit and may therefore be wasted even when power supply to said terminal unit is unnecessary.